feat: add introduction with observable and side effects operator

.gitignore

-.idea/
\ No newline at end of file
+.idea/
+.gradle/
+gradle/
+out/
\ No newline at end of file

artifact.gradle

+version = "1.0.0"
+group = "com.ippon.codingdojo"
\ No newline at end of file

build.gradle

+plugins {
+    id 'java'
+}
+
+apply from: 'artifact.gradle'
+
+sourceCompatibility = 1.8
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+
+    implementation "io.reactivex.rxjava2:rxjava:2.2.1"
+
+    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.1.1'
+    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.1.1'
+}
+
+test {
+    useJUnitPlatform()
+}
\ No newline at end of file

gradlew

+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"

gradlew.bat

+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

settings.gradle

+rootProject.name = 'reactive'

src/main/java/com/ippon/codingdojo/App.java

+package com.ippon.codingdojo;
+
+public class App {
+
+  public static void main(String[] args) {
+
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part1/Code1.java

+package com.ippon.codingdojo.reactive.part1;
+
+import io.reactivex.Observable;
+import java.util.Arrays;
+import java.util.List;
+
+public class Code1 {
+
+  public static void main(String[] args) {
+    final List<String> names = Arrays.asList("Alice", "Bob", "John");
+    final Observable<String> observable = Observable.fromIterable(names);
+    observable.subscribe(System.out::println);
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part1/Code2.java

+package com.ippon.codingdojo.reactive.part1;
+
+import io.reactivex.Observable;
+import java.util.Arrays;
+import java.util.List;
+
+public class Code2 {
+
+  public static void main(String[] args) {
+    final List<String> names = Arrays.asList("Alice", "Bob", "John");
+    final Observable<String> observable = Observable.fromIterable(names);
+    observable
+        .map(String::toUpperCase)
+        .filter(name -> name.length() > 3)
+        .map(name -> "Hello " + name)
+        .subscribe(System.out::println);
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code1.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+import java.util.Arrays;
+import java.util.Collection;
+
+public class Code1 {
+
+  private static Collection<String> NAMES = Arrays.asList("John", "Alice", "Bob");
+
+  public static void main(String[] args) {
+
+    Observable
+        .fromArray("John", "Alice", "Bob")
+        // print messages for each name in the stream and for stream completion
+        // Hint: doOnNext, doOnComplete ...
+        .subscribe();
+
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code1Solution.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code1Solution {
+
+  public static void main(String[] args) {
+
+    Observable
+        .fromArray("John", "Alice", "Bob")
+        .doOnNext(System.out::println)
+        .doOnComplete(() -> System.out.println("onComplete()"))
+        .subscribe();
+
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code2.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code2 {
+
+  public static void main(String[] args) {
+
+    Observable
+        .fromArray("John", "Alice", "Bob")
+        .map(name -> {
+          if (name.length() <= 3) {
+            throw new RuntimeException("Name length should be greater than 3");
+          }
+          return name;
+        })
+        // print messages for each name in the stream and for stream completion, and stream error
+        // Hint: doOnNext, doOnComplete, doOnError ...
+        .subscribe();
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code2Solution.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code2Solution {
+
+  public static void main(String[] args) {
+    Observable
+        .fromArray("John", "Alice", "Bob")
+        .map(name -> {
+          if (name.length() <= 3) {
+            throw new RuntimeException("Name length should be greater than 3");
+          }
+          return name;
+        })
+        .doOnNext(System.out::println)
+        .doOnError(e -> System.out.println("Ouuups : " + e.getMessage()))
+        .doOnComplete(() -> System.out.println("onComplete()"))
+        .subscribe();
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code3.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code3 {
+
+  public static void main(String[] args) {
+
+    Observable
+        .fromArray("John", "Alice", "Bob")
+        .map(name -> {
+          if (name.length() <= 3) {
+            throw new RuntimeException("Name length should be greater than 3");
+          }
+          return name;
+        })
+        // Do the same as in Code2 by using doOnEach() operator only
+        .subscribe();
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code3Solution.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code3Solution {
+
+  public static void main(String[] args) {
+
+    Observable
+        .fromArray("John", "Alice", "Bob")
+        .map(name -> {
+          if (name.length() <= 3) {
+            throw new RuntimeException("Name length should be greater than 3");
+          }
+          return name;
+        })
+        .doOnEach(notification -> {
+          if (notification.isOnNext()) {
+            System.out.println(notification.getValue());
+          } else if (notification.isOnError()) {
+            System.out.println("Ouuups : " + notification.getError().getMessage());
+          } else if (notification.isOnComplete()) {
+            System.out.println("onComplete()");
+          }
+        })
+        .subscribe();
+
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code4.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code4 {
+
+  public static void main(String[] args) {
+    Observable
+        .fromArray("John", "Alice", "Bob")
+        // Print message, errors, and completion by using subscribe method parameters
+        .subscribe(/* ... */);
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code4Solution.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code4Solution {
+
+  public static void main(String[] args) {
+    Observable
+        .fromArray("John", "Alice", "Bob")
+        .subscribe(
+            System.out::println,
+            e -> System.out.println("Ouuups : " + e.getMessage()),
+            () -> System.out.println("onComplete()")
+        );
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code5.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code5 {
+
+  public static void main(String[] args) {
+
+    final Observable<String> observable = Observable.create(subscriber -> {
+      // Emit item and notify the completion by using subscriber methods ...
+      // Hint: onNext(), onComplete()
+    });
+
+    observable
+        .subscribe(
+            System.out::println,
+            e -> System.out.println("Ouuups : " + e.getMessage()),
+            () -> System.out.println("onComplete()")
+        );
+
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code5Solution.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code5Solution {
+
+  public static void main(String[] args) {
+
+    final Observable<String> observable = Observable.create(subscriber -> {
+      subscriber.onNext("Alice");
+      subscriber.onNext("John");
+      subscriber.onNext("Bob");
+      subscriber.onComplete();
+    });
+
+    observable
+        .subscribe(
+            System.out::println,
+            e -> System.out.println("Ouuups : " + e.getMessage()),
+            () -> System.out.println("onComplete()")
+        );
+
+  }
+
+}

src/main/java/com/ippon/codingdojo/reactive/part2/Code6.java

+package com.ippon.codingdojo.reactive.part2;
+
+import io.reactivex.Observable;
+
+public class Code6 {
+
+  public static void main(String[] args) {
+
+    final Observable<String> observable = Observable.create(subscriber -> {
+      // Complete code in order to see the following output:
+      // Alice
+      // John
+      // Ouuups : BAZINGA
+
+      //Hints: onNext(), onComplete(), onError()
+    });
+
+    observable
+        .subscribe(
+            System.out::println,
+            e -> System.out.println("Ouuups : " + e.getMessage()),
+            () -> System.out.println("onComplete()")
+        );
+
+  }
+
+}